High Arch Dam Research Articles

Seismic stability analysis of a high arch dam-foundation system considering ground motion and modeling parameter uncertainties

In this research, seismic stability uncertainty analysis of a high arch dam-foundation system is investigated considering ground motion and modeling parameter uncertainties. Ground motions and modeling parameters of shear strength on the potential sliding block of dam abutment are chosen as random variables in the probabilistic and statistic framework. Taking a high arch dam as a case study, a total number of 1000 nonlinear dynamic analyses are performed using incremental dynamic analysis (IDA) and Latin hypercube sampling (LHS). The peak ground acceleration (PGA) is taken as intensity measure (IM) and the residual sliding displacement and sliding area ratio are adopted as seismic sliding stability performance evaluation indexes, respectively. Comparative analyses are presented to discuss the effect of only modeling parameter uncertainty, only ground motion uncertainty, and both uncertainties on seismic sliding stability of the high arch dam-foundation system. The results reveal that obvious variability of seismic sliding stability of the high arch dam-foundation system is observed due to the existence of ground motion and modeling parameter uncertainties and it is sensitive to PGA. The variability owing to both ground motion and modeling parameter uncertainties is more remarkable compared with that caused by only one single uncertainty. Moreover, the ground motion uncertainty shows a more obvious impact on the variability of residual sliding displacement, while the modeling parameter uncertainty has a more notable effect on the variability of sliding area ratio. Therefore, it is necessary to consider both two kinds of uncertainties for seismic stability safety evaluation of a high arch dam-foundation system in the probabilistic and statistic framework.

Analysis of deformation and leakage performance of Xiluodu reservoir dam foundation using a coupled two-factor stress-deformation-seepage model

The data for the 285.5 m high Xiluodu reservoir arch dam, China's second-largest, from 2012 to 2021 was monitored and analyzed to assess river valley contraction deformation and dam foundation leaks. The in situ stress had a significant impact on the fractured rock mass deformation characteristics, and the deformation had a strong influence on the rock mass permeability and its seepage behavior characteristics. A deterministic coupling relationship between dam foundation seepage, stress, and river valley deformation was developed. The stress–deformation behavior was consistent with the Kelvin model of the elastic–plastic deformation of rock masses, and the relationship between seepage and deformation obeyed Darcy's law. The proposed coupled two-factor relationships were useful for predicting river valley contraction. The developed models successfully computed the valley contractions associated with deformation and dam foundation leaks with R2 values >0.98 between the modeled results and measured data. This study offers value in the prediction of upstream and downstream river valley contractions after impoundment and can be used as a tool in proposing control measures to alleviate future anticipated problems.

A Hybrid Feature Selection-multidimensional LSTM Framework for Deformation Prediction of Super High Arch Dams

Developing a deformation prediction model with strong robustness and applicability based on monitoring data is an important task in establishing a safety monitoring system for super high arch dams. This study proposes a hybrid deep learning (DL) model for deformation prediction, named HFS/xs-MLSTM. The proposed multidimensional long short-term memory (MLSTM) DL achieves integrated modeling of two factors, environment and temporal correlation, by constructing a multivariate matrix, and achieves sequential prediction by rolling through the sliding windows. This operation solves the problem of insufficient prediction accuracy due to the traditional method considering only a single factor. To address the problems of computational time consumption and DL overfitting caused by variable redundancy, a hybrid feature selection method (HFS/xs) based on eXtreme gradient boosting and Spearman is proposed. Analysis shows that HFS/xs can comprehensively reflect the intrinsic laws of the data and effectively filter out the most concise set of variables, which greatly improves the operability and stability of MLSTM. Compared with traditional methods, HFS/xs-MLSTM has the best performance and applicability for deformation prediction in different zones and operating conditions. This study can provide reliable a priori knowledge for the construction of safety monitoring system for super high arch dams.

Quantitative analysis method for the importance of stress influencing factors of a high arch dam during the operation period using SPA–OSC–PLS

Quantitative analysis method for the importance of stress influencing factors of a high arch dam during the operation period using SPA–OSC–PLS

Optimized multi-output LSSVR displacement monitoring model for super high arch dams based on dimensionality reduction of measured dam temperature field

Establishing a reasonable displacement health monitoring model is essential for determining the safety of super high arch dams. However, previous studies only focus on a single measurement point, which leads to low efficiency and accuracy problems in evaluating the overall status of the dam. To solve this issue, a multi-output least square support vector regression (MLSSVR) model that can evaluate and forecast multiple monitoring points is developed in this manuscript. The optimal parameters of the model are determined by particle swarm optimization (PSO), in order to improve the precision and generalization ability of the model. On the other hand, the kernel principal component algorithm (KPCA) is introduced to extract the principal temperature components to construct the model, which brings advantages in revealing the actual temperature displacement accurately compared to the harmonic function and ambient temperature, as well as overcoming the multicollinearity caused by the superabundant of temperature factors. The feasibility and accuracy of the proposed model are tested with long-term measured displacements of a super high arch dam. The results show that the proposed model is superior to the multiple linear regression (MLR) and support vector regression (SVR), based on the hydrostatic-seasonal-time (HST) and hydrostatic-temperature–time (HTT) models. It also has outstanding medium and long-term predictive capacity, which provides a new approach for dam displacement safety monitoring.

A new endurance time analysis method for damage evaluation of high arch dams under the oblique incidence of mainshock-aftershock seismic sequences by wavelet decomposition

Pulse and oblique incidence features that may be generated by near-fault seismic sequences are neglected in current earthquake-resistant design codes for arch dams. To solve the shortcomings of endurance time analysis method which cannot consider near-fault pulse-like ground motions, this paper attempted to develop a new endurance time analysis method by wavelet decomposition to assess the differences in damage mechanisms of arch dams under the cross-stream and stream oblique incidences of near-fault seismic sequences. This study decomposed a typical near-fault earthquake into high-frequency and low-frequency ground motion through wavelet decomposition, which is used to perform several nonlinear dynamic analyses under different seismic intensities and seismic sequence incidence angles. On the basis of dynamic calculations, the local and global damage indices of the dam were presented, with a focus on the comparison of the damage distribution and damage volume ratios of arch dams under the action of single and sequence earthquakes and by analysing the damage mechanisms of arch dams under two diagonal incidence conditions at different peak accelerations. Then, the effects of different frequency components of ground motions on dam damage indices were compared, and finally, additional damage to the dam after the mainshock damage was quantified for various aftershocks. The proposed novel prediction model was used to estimate aftershock damage by considering mainshock damage. The numerical results indicate that the dam damage development is highly complex during original mainshock cross-stream and stream oblique incidences. This finding differs from dam damage that spread from the downstream face to the upstream face during the vertical incidence. The dam damage degree is smaller for the original mainshock stream oblique incidence than for the original mainshock cross-stream oblique incidence. The original aftershock induces stronger damage requirements on the damaged dam during the mainshock than during the high-frequency aftershock. Original and high-frequency seismic sequences with cross-stream and stream oblique incidences do not contribute to variations in dam damage patterns during aftershocks. Therefore, the influence of near-fault pulse impacts and the oblique incidence angle of seismic sequences need to be considered comprehensively in the seismic calculations and reinforcement studies of arch dams.

Impinging pressure and flood discharge atomization in high arch dams with flaring gate piers

This study discusses the effects of geometrical parameters of flaring gate piers, such as contraction ratio, sidewall extension ratio and plunge angle, on the impinging pressure and flood atomization based on hydraulic model tests and atomization simulations. It is found that the impinging pressure decreases and the length of rainstorm increases with the increasing impact collision of aerated jets. Decreasing the plunge angle and increasing the extension length of sidewall for violent collision should be considered in the design stage and protection measures for rainstorms should be taken into account. Reducing the atomization hazard by collision avoidance could be selected in the operational phase on the premise of safety factor of plunge pool. A simplified formula is developed to predict the length of rainstorm as a function of the maximum impinging pressure, for use as a reference in the design and modification of similar projects.

Petrophysical Properties of Tight Marl Reservoir and Its Influence on Fluid Percolation Capacity

Tight marl reservoir has always been a essential place for oil and gas storage in geophysical exploration. The oil under the Marl reservoir is a essential oil and gas storage resource in geophysical research, which accounts for more than half of all oil and gas resources. The marl reservoir has the characteristics of strong heterogeneity, complex lithology, and complex reservoir system, because most of them are buried deep underground, the research risk and cost are very high. In the past decade, most of the low-speed oil and gas resources developed in oil and gas fields have been exhausted, so the marl area has become an important distribution area of oil and gas research. This paper mainly studies the petrophysical properties of tight marl oil and gas reservoir and its influence on fluid percolation capacity. Through studying the characteristics of marl, it has the petrophysical properties of oil and gas reservoirs, pre-stack seismic inversion of shale oil and gas reservoirs, further exploration of natural resources, and its use to better benefit mankind. In this paper, the core sample basic parameter measurement, stress model, rock rheological force, petrophysical application method and related experiments are used to study the petrophysical properties of tight marl oil and gas reservoir and its influence on fluid percolation capacity, which is of great significance to the long-term stability of high arch dam, And the utilization and production of natural resources are of great practical engineering significance and social significance. The results show that the rock content varies about 5% in different rock physical properties, which shows different fluid percolation capacity. In the analysis of marl oil and gas reservoirs, it has important theoretical significance and engineering value to analyze the rheological effect of seepage field and stress field of dam bedrock under long-term load.

Study on influence of construction and water storage process on valley deformation of high arch dam

Study on influence of construction and water storage process on valley deformation of high arch dam

Vibration load identification in the time-domain of high arch dam under discharge excitation based on hybrid LSQR algorithm

The identification of vibration load is of great importance in studying the vibration induced by discharge of high arch dam. Considering the ill-posedness in time-domain identification of vibration load, a hybrid least squares QR (LSQR) iterative identification method is proposed. The system response is expressed as the convolution of the unit impulse response function and the excitation load. It is discretized into a set of linear equations, and the mathematical model of the inverse problem of load identification is established. On the basis of vibration signal filtering and noise reduction, Tikhonov regularization method is used to pre optimize LSQR iterative algorithm. This process is performed because the LSQR algorithm is prone to nonconvergence when the error of observation data is large. Thus, a hybrid LSQR algorithm is obtained to improve the ill-posedness of the inverse problem. Numerical examples show that the proposed method can recognize multiple vibration loads effectively and stably under different noise levels, and the recognition accuracy is better than the conventional regularization method. The proposed method is applied to an engineering example. Results show that the proposed method is feasible and effective for the time-domain identification of vibration load of a high arch dam.

Ensemble Learning-Aided Hydrothermal Coupling Investigation on Dam Impoundment Impact: A Case Study of the Xiluodu Project in China

Abstract The monitoring and analysis of the temperature field in the reservoir area is gaining importance as it provides insights regarding structural safety and environmental impact. Most studies focus on earthen dams and the seasonal fluctuation of the thermal field induced by the ambient temperature. Few studies analyse the long-term trend of the bedrock temperature after high-arch dam impoundment as the involved geological elements are likely to be unexpected and unknown. In this paper, a unique geothermal evolution model in the downstream bedrock of a 285.5 m high-arch dam is reported based on continuous field observations during the past nine years, which cannot be explained by available hydrogeological data. To clarify the phenomenon, a research framework that comprises field measurements, machine learning interpretation, and hydrothermal coupling simulation is proposed. Borehole surveys and water chemistry analyses are performed to gather more data from critical areas. The proposed machine learning pipelines attempt to interpret the field test data. These are integrated with a double-loop grid-search process and can achieve hyperparameter searching and model evaluation simultaneously. It proves to be robust to local minima and more applicable to groundwater source discrimination when compared to other models. The contribution of the newly discovered features is further discussed through comparative and sensitivity analysis based on the hydrothermal coupling theory. With the proposed hybrid analysis framework, the shallow buried limestones and the confined hot groundwater have been identified as the causes of the unique phenomenon. These factors should be of concern to researchers facing similar situation in the future.

Comparison of the Seismic Responses of an Arch Dam under Excitation from the Design Response Spectrum in the New and Old Chinese National Standards

The new Chinese national standard, Standard for the seismic design of hydraulic structures (GB51247-2018), has been published. Compared with the Specifications for the seismic design of hydraulic structures (SL203-1997), the standard design response spectrum curve was revised in the new national standard. In order to compare the seismic responses of an arch dam under excitation from the design response spectrum in the new and old standards, the dynamic calculation of a 240 m high arch dam is carried out by a three-dimensional finite element method. In the dynamic calculation, the B-differentiable equation is used to simulate the tension motion of arch dam contraction joints, and the multi-transmitting boundary method and the Westergaard added mass method are used to simulate the dam–infinite foundation and dam–reservoir interactions, respectively. The results show that the dynamic stress responses of the arch dam under excitation from the design response spectrum in the new standard are increased compared with those of the old standard. The seismic safety of an arch dam may decrease under excitation from the design response spectrum in the new standard. Thus, the seismic validation on built arch dams should be carried out by using the new standard when it is possible.

The effects of initial stresses on nonlinear dynamic response of high arch dams subjected to far-field underwater explosion

Blast performance assessment of 300 m high arch dams is an important topic having been extensively studied in recent years. Because the arch dam is convex on the upstream face, the dam body is mainly in a compressive stress state under the action of upstream water pressure. However, due to the complexity of the problem, the initial stress is ignored in the blast response analysis of arch dams. For this purpose, the influence of initial stress on nonlinear dynamic response and failure modes of a 300 m high arch dam to the far-field underwater explosion has been studied in this paper. The acoustic-structural approach is employed to model the underwater explosion loading and the dam-reservoir-foundation interaction. The Concrete Damage Plasticity (CDP) model including the strain rate effect is used to model the concrete material behavior to blast loading. Damage development processes of high arch dams to the far-field underwater explosion are investigated. Nonlinear dynamic response characteristics of high arch dams with different initial stress states subjected to the far-field underwater explosion are discussed in terms of damage modes, residual displacement, and damage dissipated energy. The results show that the initial stress has a significant influence on the nonlinear dynamic and failure modes of high arch dams to the far-field underwater explosion. The initial stress state of high arch dams under hydrostatic pressure and deadweight should be the basic condition of blast response analysis.

Mechanical Properties of Soil-Rock Mixture Filling in Fault Zone Based on Mesostructure

Soil-rock mixture (SRM) filling in fault zone is an inhomogeneous geomaterial, which is composed of soil and rock block. It controls the deformation and stability of the abutment and dam foundation, and threatens the long-term safety of high arch dams. To study the macroscopic and mesoscopic mechanical properties of SRM, the development of a viable mesoscopic numerical simulation method with a mesoscopic model generation technology, and a reasonable parametric model is crucially desired to overcome the limitations of experimental conditions, specimen dimensions, and experiment fund. To this end, this study presents a mesoscopic numerical method for simulating the mechanical behavior of SRM by proposing mesoscopic model generation technology based on its mesostructure features, and a rock parameter model considering size effect. The validity and rationality of the presented mesoscopic numerical method is experimentally verified by the triaxial compression tests with different rock block contents (RBC). The results indicate that the rock block can increase the strength of SRM, and it is proved that the random generation technique and the rock parameter model considering size effect are validated. Furthermore, there are multiple failure surfaces for inhomogeneous geomaterial of SRM, and the angle of the failure zone is no longer 45°. The yielding zones of the specimen are more likely to occur in thin sections of soil matrix isolated by blocks with the failure path avoiding the rock block. The proposed numerical method is effective to investigate the meso-damage mechanism of SRM.

A Deformation Prediction Model of High Arch Dams in the Initial Operation Period Based on PSR-SVM-IGWO

The deformation prediction of the dam in the initial stage of operation is very important for the safety of high dams. A hybrid model integrating chaos theory, support vector machine (SVM), and an improved Grey Wolf Optimization (IGWO) algorithm is developed for deformation prediction of dam in the initial operation period. Firstly, the chaotic characteristics of the dam deformation time series will be identified, mainly using the Lyapunov exponent method, the correlation dimension method, and the Kolmogorov entropy method. Secondly, the SVM-IGWO model based on phase space reconstruction (PSR) is established for deformation forecasting of the dam in the initial operation period. Taking SVM as the core, the deformation time series is reconstructed in phase space to determine the input variables of SVM and the GWO algorithm is improved to realize the optimization of SVM parameters. Finally, take the actual monitoring displacement of Xiluodu super-high arch dam as an example. The engineering application example shows that, compared with the existing models, the prediction accuracy of the PSR-SVM-IGWO model established in this paper is improved.

Performance-improved TSVR-based DHM model of super high arch dams using measured air temperature

Considering that the displacement of super high arch dams is sensitive to temperature variations and dam temperature field is essentially modulated by the ambient temperature, a measured air temperature-based hydrostatic-thermal-time (HTT) displacement health monitoring (DHM) model of super high arch dams is proposed. To fully explore the complex nonlinearity between dam displacement and its explanatory variables and to improve the predictive accuracy of the model, twin support vector regression (TSVR) is introduced to establish HTT model. Due to the influence of TVSR parameters on model performance, a performance-improved TSVR is proposed by utilizing grey wolf optimizer (GWO) algorithm to determine the optimal TSVR parameters in this study. The availability of the proposed model is tested with measured data of a super high arch dam. Results show that, compared with the harmonic functions in the commonly-used hydrostatic-seasonal-time (HST) models, the detailed variation characteristics of thermal displacement can be better captured with the measured air temperature factors in the proposed HTT model. Meanwhile, the fitting and predicting accuracy of the performance-improved TSVR-based DHM model is significantly improved. And the proposed model has an excellent long-term predictive capability. The conclusion can be drawn that the proposed model is feasible and effective for the analysis and prediction of dam displacement.

Study on deformation of abutment and the influence on high arch dam during impoundment

High arch dams in China have been impounded and entered the operation stage in succession. The value and law of deformation during impoundment are different, which brings a great challenge to the performance and long-term safety of the arch dam. Based on the analysis of monitoring data of Jinping No.1 arch dam and Xiluodu arch dam, it is pointed out that the valley width deformation is irreversible plastic deformation, and there are two modes of valley width deformation of dam foundation: bank slope deformation mode and overall deformation mode. The bank slope deformation mode shows that the valley width of the upstream is significantly larger than that of the downstream, and the chord length of the dam is not large. Based on the principle of effective stress, the deformation mechanism of bank slope deformation mode is discussed. The overall deformation mode shows that the valley width of the upper and lower reaches is similar and the magnitude is large, and the chord length of the dam is large. The boundary displacement method is used to simulate the overall deformation mode. The model of Baihetan arch dam is established, and the structural model and geological conditions of the dam site are simulated in detail. Based on 3D nonlinear finite element calculation, the effects of two valley width deformation modes on the displacement, stress and local cracking of Baihetan arch dam are analyzed, and the calculated results are compared. The results show that the overall deformation mode can cause infinite valley width deformation, while the bank slope deformation mode can only cause limited valley width deformation. When the same valley shrinkage value is produced, the bank slope deformation mode can make the dam produce new stress concentration area, and the overall deformation mode has little effect on the dam stress, which indicates that the non-uniform deformation of the dam foundation is the key to affect the stress in the dam.

Deformation characteristics and a safety monitoring model of high arch dam affected by valley narrowing deformation

Valley narrowing deformation was monitored during the first impoundment period of some high arch dam projects in China, which may affect the working behavior of dams. Dam deformation upstream was one of the most intuitive influences of valley narrowing deformation on arch dam, which makes dam safety evaluation difficult. In this paper, based on detailed monitoring data of a high arch dam project, the temporal-spatial evolution characteristics, and the mutual relationship of valley and dam deformation were analyzed. The influence of valley narrowing deformation on dam deformation was simulated by 3D Finite Element Method (FEM). According to the analysis results, an arch dam deformation safety monitoring model, considering the effect of valley deformation, was established in which the dam deformation was decomposed as water pressure, temperature, valley deformation, and time-effect components. Further, the typical process of valley deformation was analyzed using the proposed model and the decomposed components were separated. Research shows that the safety monitoring model can express the influence of various components on arch dam deformation comprehensively, and monitor the dam deformation quickly and accurately. The proposed model can be used to analyze and predict the arch dam deformation, and evaluate the dam behavior.

Optimization design of a large-scale seepage control system at a high arch dam site

The Baihetan Hydropower Station, located in the lower reaches of Jinsha River in southwest China, is the second largest hydropower station in the world. The site is characteristic of extremely complex geological and hydrogeological conditions, with fractures, faults, and shear zones that make water tables wedge-shaped. A large-scale seepage control system that contains grouting curtains covering an area of 780,000 m2 and 12,300 drainage holes, together with concrete plugs, were designed to control the seepage in the dam foundation and in the underground powerhouse areas as the reservoir water level will be raised by 225 m during operation. How to assess the performance and optimize the design of seepage control system becomes a key technological issue in the design and construction of this project. In this study, a three-dimensional finite element model that well represents the site conditions is established. The drainage holes are modelled with a substructure technique and the seepage field is solved with the variational inequality method of Signorini’s type. A procedure is proposed to optimize the layout of the seepage control system by taking the amount of leakage, the distribution of uplift pressure, the risk of seepage erosion and cost into account. Numerical results yield the appropriate parameters for the seepage control system, including the extension and depth of grouting curtains, and the spacing of drainage holes. With these optimized parameters, the seepage control system is effective in lowering the phreatic surface and limiting the amount of leakage at the dam site.

Analysis of cracking mechanism of concrete galleries in a super high arch dam

It is essential to understand the cracking mechanism of dam galleries for the overall structural design and safety of a dam. In this study, the stress equation of the D-shaped concrete gallery is derived by the complex function method of elastic mechanics and the conformal mapping method. Based on a series of field tests, monitoring data, and three-dimensional (3D) nonlinear numerical simulation, the pattern and causes of cracks in the concrete gallery of a super high arch dam 15 m above the foundation are determined. The effects of the gallery structure, position, temperature, reservoir impoundment, curtain grouting and construction process on the tensile stress distribution and cracking risk at different stages are analyzed in detail. The gallery cracking mechanism is dominated by structural effects, loading, boundary conditions and material properties during the design, construction and operation periods. The corresponding prevention and treatment methods for cracking of concrete galleries are proposed. The 1/2 height-span catenary shaped (HSC-shaped) and smaller gallery at the downstream side with a distance to the foundation in the range of 10 to 15 m is recommended. The results in this study can provide some reference for the design and cracking prevention for dam galleries.